It has been known for a long time to use a laser as cutting tool more particularly for materials in sheet form. To that end, a laser source is available, generating a light beam, which is directed by means of mirrors towards the zone of cut. Before it reaches the plane of cut, there is interposed on its path a focussing lens whose role is to concentrate the light beam into a spot of very small diameter, which furnishes a very high density of energy. Very different materials may thus be cut out provided that the thicknesses are not too great.
Cutting is obtained by melting of the material at the spot where the beam is focussed. Such melting, as a function of the nature of the material, may generate gas, of which the drawbacks are multiple: formation of a screen in front of the beam and thus absorption of power, pollution of the environment (odour and possible toxicity), pollution along the line of cut (unaesthetic blackish marks).
In order to limit these drawbacks, suction nozzles are generally employed, consisting of a dish enveloping the beam between the focussing lens and the plane of cut and in which a slight depression is created. Although this process is satisfactory with relative nozzle/material displacements which are not very rapid, this does not apply when it is desired to cut at high speed. This is the case for example for cutting out generally fine fabrics, which may be cut out at up to 100 m/min. At such speeds, the emitted gas does not have the time to be sucked by the nozzle and it remains in contact with the material. One improvement consists in increasing the depression within the nozzle, but in that case, not only the gas but also the material is sucked. What is more serious is that the debris cut out is separated from the cutting support and may burst into flame spontaneously on passing through the defocussed beam, this obviously being seriously damaging.
The invention set forth hereinafter relates to a gas-sucking device, which eliminates all the drawbacks mentioned hereinabove.
The gist of the device according to the invention consists in suitably organizing the circulations of gas (air) at the level of the zone of cut.
The laser cutting apparatus used is known per se; it may be schematically described as comprising a laser radiation emitter, a lens for focussing said radiation, fixed in an adjustable sliding sleeve and a truncated nozzle extending said sleeve towards the material to be cut and of which the small end is located in the immediate vicinity of said material to be cut.
Such an apparatus comprises a device for evacuating the gases which is essentially constituted by a hood (hereinafter referred to as ejector) open towards the material to be cut and fixed on said sliding sleeve, in which hood are arranged the elements ensuring appropriate circulation and evacuation of a gas (air).